Aqueous cleaning processes are a mainstay of conventional domestic and industrial textile fabric cleaning methods. On the assumption that the desired level of cleaning is achieved, the efficacy of such conventional processes is usually characterised by their levels of consumption of energy, water and detergent. In general, the lower the requirements with regard to consumption of one or more of these three components, the more efficient the washing process is deemed. The downstream effect of reduced water and detergent consumption can also be significant, as this minimises the need for disposal of aqueous effluent, which can be both extremely costly and detrimental to the environment.
Such washing processes involve aqueous submersion of fabrics followed by soil removal, aqueous soil suspension, and water rinsing. In general, within practical limits, the higher the level of energy (or temperature), water and detergent which is used, the better the cleaning. One key issue, however, concerns water consumption, as this sets the energy requirements (in order to heat the wash water), and the detergent dosage (to achieve the desired detergent concentration). In addition, the water usage level defines the mechanical action of the process on the fabric, which is another important performance parameter. That is, the agitation of the cloth surface during washing, plays a significant role in releasing embedded soil. In aqueous processes, such mechanical action is provided by the water usage level in combination with the drum design for any particular washing machine. In general terms, it is found that the higher the water level in the drum, the better the mechanical action. Hence, there is a dichotomy created by the desire to improve overall process efficiency (i.e. reduce energy, water and detergent consumption), and the need for efficient mechanical action in the wash.
Various different approaches to the development of new cleaning technologies have been reported in the prior art, including methods which rely on electrolytic cleaning or plasma cleaning, in addition to approaches which are based on ozone technology, ultrasonic technology or steam technology. Thus, for example, WO2009/021919 teaches a fabric cleaning and disinfection process which utilises UV-produced ozone along with plasma. An alternative technology involves cold water washing in the presence of specified enzymes, whilst a further approach which is particularly favoured relies on air-wash technology and, for example, is disclosed in US2009/0090138. In addition, various carbon dioxide cleaning technologies have been developed, such as the methods using ester additives and dense phase gas treatments which are described in U.S. Pat. No. 7,481,893 and US2008/0223406, although such methods generally find greater applicability in the field of dry cleaning. Many of these technologies are, however, technically very complex.
In the light of the challenges which are associated with aqueous washing processes, the present applicant has previously devised a new approach to the problem that allows the deficiencies demonstrated by the methods of the prior art to be mitigated or overcome. The method which is provided eliminates the requirement for the use of large volumes of water, but is still capable of providing an efficient means of cleaning and stain removal, whilst also yielding economic and environmental benefits.
Thus, in WO2007/128962 there is disclosed a method and formulation for cleaning a soiled substrate, the method comprising the treatment of the moistened substrate with a formulation comprising a multiplicity of polymeric particles, wherein the formulation is free of organic solvents. The substrate may be wetted so as to achieve a substrate to water ratio of between 1:0.1 to 1:5 w/w, and optionally, the formulation additionally comprises at least one cleaning material, which typically comprises a surfactant, which most preferably has detergent properties. In the disclosed embodiments, the substrate comprises a textile fibre. The polymeric particles may, for example, comprise particles of polyamides, polyesters, polyalkenes, polyurethanes or their copolymers, a particular example being nylon beads.
The use of this cleaning method, however, presents a requirement for the nylon beads to be efficiently separated from the cleaned substrate at the conclusion of the cleaning operation. In addition to this problem, the present applicant also identified that the provision of means to enable continuous circulation of the nylon beads during the cleaning operation would further improve the process. These issues were addressed in WO2011/098815 wherein the present applicant provided an apparatus for use in the cleaning of soiled substrates, the apparatus comprising housing means having a first upper chamber with a rotatably mounted cylindrical cage mounted therein and a second lower chamber located beneath the cylindrical cage, and additionally comprising at least one recirculation means, access means, pumping means and a multiplicity of delivery means, wherein the rotatably mounted cylindrical cage comprises a drum having perforated side walls where up to 60% of the surface area of the side walls comprises perforations comprising holes having a diameter of no greater than 25.0 mm.
WO2011/098815 further discloses the use of the apparatus in methods for the cleaning of soiled substrates with formulations comprising solid particulate cleaning material and wash water, the methods typically comprising the steps of:                a. introducing solid particulate cleaning material and water into the lower chamber of the apparatus;        b. agitating and heating the solid particulate cleaning material and water;        c. loading at least one soiled substrate into the rotatably mounted cylindrical cage via the access means;        d. closing the access means so as to provide a substantially sealed system;        e. introducing the solid particulate cleaning material and water into the rotatably mounted cylindrical cage;        f. operating the apparatus for a wash cycle, wherein the rotatably mounted cylindrical cage is caused to rotate and wherein fluids and solid particulate cleaning material are caused to fall through perforations in the rotatably mounted cylindrical cage into the lower chamber in a controlled manner;        g. operating the pumping means so as to transfer fresh solid particulate cleaning material and recycle used solid particulate cleaning material to separating means;        h. operating control means so as to add the fresh and recycled solid particulate cleaning material to the rotatably mounted cylindrical cage in a controlled manner; and        i. continuing with steps (f), (g) and (h) as required to effect cleaning of the soiled substrate.        
As outlined in WO2011/098815 the generation of suitable G forces, in combination with the action of the solid particulate cleaning material, was found to be an important factor in achieving an appropriate level of cleaning of the soiled substrate. Thus in embodiments disclosed in WO2011/098815, the cylindrical cage is rotated at a speed of 30 to 800 rpm in order to generate G forces of 0.49 to 350.6 at different stages of the cleaning process. In one preferred embodiment disclosed in WO2011/098815, rotation of the rotatably mounted cylindrical cage is caused to occur at a G force of less than 1 during the wash cycle. Much higher G forces, for example between 10 and 1000, are disclosed to be generated only on completion of the wash cycle and to effect a measure of drying of the cleaned substrate when the feeding of solid particulate material into the cage has ceased.
Although the methods disclosed in WO2007/128962 and WO2011/098815 provided considerable improvements for the cleaning of soiled substrates with formulations comprising solid particulate material and wash water, the present inventors have recognised that there remains scope for improvement.
The present inventors have recognised the opportunity for enhanced cleaning of substrates without requiring the use of higher or additional amounts of detergent-containing cleaning agents.
The present inventors have further recognised that the solid particulate material can become localised in certain areas of the drum. Such localisation can lead to a less than optimal distribution of said particulate material throughout the soiled substrates which can lead to a limiting of the maximum obtainable cleaning performance.
The present invention seeks to provide a method for cleaning of soiled substrates with a solid particulate material that can ameliorate or overcome above-noted problems associated with the prior art.
Preferably, the present invention seeks to provide a method for cleaning of soiled substrates with a solid particulate material which can provide enhanced cleaning of the substrate.
More preferably, the present invention seeks to provide a method for cleaning of soiled substrates with a solid particulate material which can provide enhanced cleaning of the substrate and which method does not require the use of higher or additional amounts of detergent-containing cleaning agents.
Preferably, the present invention can provide a method of cleaning soiled substrates with a solid particulate material which can ameliorate or overcome one or more of the above-noted problems.
The present inventors have recognised that a cleaning method which provides an increased and/or prolonged mechanical interaction between the solid particulate material and a soiled substrate within the cleaning apparatus can facilitate an enhanced degree of cleaning of the substrate. The inventors have further recognised such a method can provide an enhanced cleaning effect without increasing the quantity of cleaning agents utilised in the cleaning process.
The present inventors have further recognised that an improved distribution of said particulate material within the drum, and more especially on entry to the drum, can provide an enhanced degree of cleaning of the substrate.
The present inventors have recognised that many of the abovementioned technical problems become more significant as the drum size is reduced (e.g. for domestic washing machines) and/or as the ullage (free space) in the drum is reduced (e.g. because the drum is highly loaded with a soiled substrate).